The invention is directed to a composite reinforcement tire cord similar to cords having a relatively weak core around which much stronger, inextensible yarns or cords are coiled, such that the composite cord has, initially, a low tensile modulus which abruptly changes to a substantially higher modulus upon predetermined elongation of the cord. The cores of the tire cords used heretofore are typically composed of either a low tensile material such as a single strand of cotton, rayon, nylon or polyester, which is readily breakable, or a vulcanized elastomeric material which is stretchable and allows the inextensible yarns to uncoil and straighten out during the toroidal shaping and molding of the tire.
The invention is directed to the provision of a composite, highly elongatable cord having a core which, at room temperature under tension, has a barrier to elongation and elastic recovery. Further, the core is composed of material that loses its tensile strength when subjected to high temperature during the molding and vulcanization operations so as to permit elongation of the yarns wrapped around the core.
Briefly stated, the invention is in a composite cord for reinforcing elastomeric articles such as tires. The composite cord comprises a plurality of substantially inextensible yarns which are spirally wrapped around a core which has an elastic limit, at low elongation, sufficient to maintain the configuration of the cord during processing, but which loses its tensile strength during the molding and vulcanization of the elastomeric article to permit extension of the cord after being subjected to the temperature of vulcanization.